Abstract We discuss the production of massive relic coherent gravitons in a particular class of ƒR gravity, which arises from string theory, and their possible imprint in the Cosmic Microwave Background. In fact, in the very early Universe, these relic gravitons could have acted as slow gravity waves. They may have then acted to focus the geodesics of radiation and matter. Therefore, their imprint on the later evolution of the Universe could appear as filaments and a domain wall in the Universe today. In that case, the effect on the Cosmic Microwave Background should be analogous to the effect of water waves, which, in focusing light, create optical caustics, which are commonly seen on the bottom of swimming pools. We analyze this important issue by showing how relic massive gravity waves GWs perturb the trajectories of the Cosmic Microwave Background photons gravitational lensing by relic GWs. The consequence of the type of physics discussed is outlined by illustrating an amplification of what might be called optical chaos. View Full-Text